1. Field of the Invention
This invention relates to a roller guide method and system for guiding steel materials between guide rollers into a rolling mill machine to roll the steel materials to linear steel products having various sectional shapes such as wire rods, various steel bars, and section steels including an H-section beam, while preventing the steel material from tilting in a nip space defined between the guide rollers in the course of rolling.
2. Description of the Prior Art
A conventional roller guide apparatus for guiding a steel material to be rolled to linear steel products, section steel products and such has a mere function of preventing miss-rolling possibly caused by failure of introducing the steel material thereinto. However, it has been known that the conventional roller guide apparatus cannot disadvantageously satisfy the recent rigorous demands for accuracy in sectional shape and size of rolled steel products resultantly obtained. To be concrete, the conventional apparatus cannot achieve the accuracy in roundness of a wire rod or other dimensional accuracy of the rolled steel products when the steel material to be rolled is nipped and guided between the guide rollers on a tilt into a subsequent rolling mill machine.
Thus, there have been so far proposed methods for effectively preventing the miss-rolling and tilting of the steel material as specified above in the course of rolling. One of the proposed prior art methods is disclosed in Japanese Patent Publication No. SHO 60-40933 (hereinafter referred to as "First Prior Art") for a guiding method for a steel material to be rolled. In this method, in order to reliably introduce a wire rod of steel material into a nip space defined between guide rollers and further prevent tilting of the wire rod in the nip space, the guide rollers between which the wire rod is guided are kept somewhat apart from each other to leave the nip space wider than the diameter of the wire rod to be passed until the leading end of the wire rod reaches the guide rollers, and then, the guide rollers are brought close to each other to narrow down the aforesaid nip space when the leading end of the wire rod enters in between the guide rollers. After the tail end of the wire rod has passed therethrough, the nip space between the guide rollers is brought to the status quo ante.
Also, Japanese Patent Application Public Disclosure No. SHO 52-66865 (hereinafter referred to as "Second Prior Art") discloses a roller guide apparatus capable of nipping a steel material between guide rollers with a prescribed load in the course of rolling so as to accomplish precision rolling. Other methods of imparting prestress (preload) to a roller guide apparatus to increase the rigidity of the apparatus are disclosed in Japanese Utility Model Publications Nos. SHO 39-24250 ("Third Prior Art") and SHO 61-1929 ("Fourth Prior Art").
The guiding method of the First Prior Art as noted above adopts the idea of imparting an "embracing force" for nipping the steel material with the rollers. However, it has been experimentally known that a wire rod may possibly tilt even when being applied with the embracing force as a matter of fact. There has been generally believed the cause such that, in order to cope with the present day tendencies in rolling toward application of high-strength steel materials or high-deformation resistance steel materials such as special steel and diversified small-quantity production of rolled steel products, even a roller guide apparatus essentially suitable for specific rolling commonly tends to be applied to various rolling systems for high-speed rolling and high-load rolling such as low temperature rolling, which are effected under different conditions for producing rolled steel products of varied kinds, consequently suffering from increased load. The First Prior Art discloses the use of the hydraulic system for increasing the embracing force with which the steel material is retained between the guide rollers. However, the hydraulic system used therein is controlled to assume either its operative ON state or its inoperative OFF state. As a result, the embracing force produced by the hydraulic system is maintained just constant in the state of nipping the steel material between the guide rollers. The constant embracing force signifies that the roller guide system composed of the guide rollers is formed of a substantially non-rigid, flexible structure. Such a flexible structure offers no elastic resistance to the force to cause the guide rollers to be push open, which is produced by the steel material tilting, even when the steel material nipped between the guide rollers begins to have a tilt, whereby tilting of the steel material in the nip space between the guide rollers cannot be prevented.
Even in the Third Prior Art and Fourth Prior Art both teaching the method for application of prestress, increments determined stepwise in rigidity of the roller guide apparatus are not sufficient for meeting the severe rolling conditions of late years. Thus, these prior art also cannot prevent the steel material from inevitably tilting between the guide rollers.
Every prior art entails a disadvantage such that tilting of the steel material to be rolled to linear steel products including wire rods and steel bars or section steel products inevitably occurs, consequently giving rise to inconveniences of miss-rolling or deterioration of dimensional accuracy in sectional shape and size of the rolled steel product.